Moisture indicator for photoflash lamp



July 18, 1961 R. M. ANDERSON 2,993,003

MOISTURE INDICATOR F OR PHOTOFLASH LAMP Filed May 21, 1958 Irwvervtov: Rober l; M. Anci vson, b Mar [j 8 His Al? ovneg.

United States This invention relates in general to photoflash lamps and similar devices comprising a sealed envelope, and more particularly to the provision therein of means for determining the presence of air or other foreign material.

Photographic flash lamps most generally available on the market today comprise a sealed glass envelope or bulb having a charge of readily combustible material arranged within the bulb portion of the envelope, at filling of combustion supporting gas such as oxygen, and ignition means comprising a pair of lead-in wires extending substantially straight through the envelope from the neck end of the bulb and bridged at their inner ends by a filament, the ends of which are embedded in beads of primer or fulminating material coated on the inner end portions of the lead-in wires. The combustible material generally consists of shredded metallic foil. The beads of primer on the ends of the lead-in wires are extremely sensitive and when the filament is heated by the passing of electric current therethrough, the beads ignite, which, in turn, ignite the combustible material.

Occasionally, during or following manufacture thereof, a photoflash lamp will develop a leak, and the combustion supporting gas therein will become contaminated with atmospheric gas. Such a lamp is defective and will not flash properly when ignited as described above. Further, when the leak in the lamp is slow it may require a considerable period of time after manufacture before the combustion supporting gas in the lamp is sufficiently contaminated to detect the presence of the contaminating gas.

It is already known that various salts of cobalt may be used in a photoflash lamp as an indicator for the presence of contaminating air; the complex salt cobaltous-cobaltic cyanide is particularly sensitive for detecting such contaminating gas. Such a cobalt salt depends upon the moisture in the contaminating air for creating a change in color of the salt. In the anhydrous state, the salt is blue; in the hydrated state, the salt is pink.

However, difliculty has been experienced with the cobaltous-cobaltic cyanide in that it tends to flake away from the bulb or surface upon which it is applied during the sealing-in operation of the lamp, particularly where the flash lamp has no lacquer coating on the inside to constitute a layer to which the indicator will readily adhere. Therefore, various agents have been tried as binders for the cobalt salt. Certain binders decreased the moisture indicating properties of the cobaltous-cobaltic cyanide; other binders were deliquescent and would take any moisture present away from the cobaltous-cobaltic cyanide and considerably decrease its moisture indicating properties.

It is therefore an object of the present invention to provide an improved binder for cobaltous-cobaltic cyanide when used as a moisture indicator in a photoflash lamp.

According to the invention, it was found that barium chloride had the unique property of not afiecting the moisture indicating quality of cobaltous-cobaltic cyanide; and could be used both as a binder and a filler for the aforementioned complex cobalt salt. Barium chloride is found to actually increase the sensitivity of some of the mixtures of cobaltous-cobaltic cyanide. The use of barium chloride as a filler for the cobaltous-cobaltic cyanide salt has the further advantage in the reduction of cost of the composition; the cobaltous-cobaltic cyanide being approximately eleven times the cost of the barium chloride.

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Other objects and advantages of the invention will become evident as the following description proceeds, and from a reference to the accompanying drawing.

The single figure of the drawing is an elevation, partly in section, of a photoflash lamp provided with a moisture indicator according to the present invention.

In the specific embodiment illustrated in the drawing, a glass or other transparent bulb 1 is set in a base 2. Hermetically sealed within the bulb 1 is a stem 3 supporting lead-in wires 4 across which is secured an ignition filament 5 which is capable of igniting bead 6 of primer material. The ignition of the primer material 6 in turn is capable of flashing the combustible material 7 which is herein illustrated as shredded material, for example, shredded metallic foil of such material as aluminum, magnesium, or zirconium. An appropriate combustion supporting gas, for example, oxygen, is contained within the lamp.

In the usual manufacture of such a lamp, the bulb is loaded with the combustible material 7 and ignition means is assembled therewith. The bulb is then evacuated and charged with the combustion supporting gas, and then sealed in accordance with known methods.

According to the present invention, an indicating spot 8 of composition constituting the present invention is applied within the bulb, for example, on the inner surface thereof, for the aforesaid purpose prior to the loading of the combustible material. It was found that the moisture indicator 8 could constitute a mixture of cobaltous-cobaltic cyanide with from 5% to 80% by weight of the total weight of the mixture of barium chloride, suspended in an appropriate vehicle. The vehicle is ultimately evaporated and is not present in the sealed-off bulb. It was found that the mixture would be adequately dried by evacuation of the lamp during manufacture to change the indicator from pink to blue without any further process needed.

By way of example, but not limitation, a suitable indicator mixture may be made by combining by weight of barium chloride to 25% by weight of cobaltouscobaltic cyanide and adding to this mixture an appropriate amount of a liquid vehicle, such as Water or a mixture of water and methyl alcohol or a mixture of water and butyl alcohol, or the like. A mixture having these proportions may be made by combining 3 gm. of barium chloride, 1 gm. of cobaltous-cobaltic cyanide, and 4 gm. of water as the liquid vehicle. After the paste is made, the spot of indicator is applied at the desired position on the inside of the bulb, after which the bulb is loaded with the combustible material, the ignition means are assembled therewith, the lamp is evacuated and charged with the usual combustion supporting gas, and the lamp is then scaled up. In the event that the bulb is a leaker, and admits contaminating atmospheric gas, including moisture in the gas, the cobalt salt will change from a blue color to a pink color.

The amount of barium chloride used depends largely upon the degree of blueness wanted when the leak indicator is in its anhydrous state. The specific example using 75% by Weight of barium chloride produces enough color change in the spot to detect the presence of moisture; suflicient color change occurs throughout the above mentioned range of 5 to by weight of barium chloride in the total weight of the barium chloride cobaltouscobaltic cyanide mixture. Of course, as the concentration of the barium chloride increases, the moisture indicating spot becomes a lighter blue when in an anhydrous state and a lighter pink in the hydrated state.

Barium chloride then produces an excellent binder to adhere cobaltous-cobaltic cyanide moisture indicator to the inside of a photoflash bulb; and serves as a filter for the aforementioned complex cobalt salt to thereby reduce the cost of the mixture.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A moisture indicating material for inclusion in the envelope of a lamp to indicate by change in coloration the presence of air therein, said indicating material being composed of a mixture consisting substantially of cobaltous-cobaltic cyanide and 580% by weight of a binder of barium chloride.

2. A mositure indicating material for inclusion in the envelope of a lamp to indicate by change in coloration the presence of air therein, said indicating material being composed of a mixture consisting essentially of approximately 25% by weight of cobaltous-cobaltic cyanide and approximately 75% by Weight of a binder of barium chloride.

References Cited in the file of this patent UNITED STATES PATENTS Toch Feb. 17, 1931 Smith Apr. 8, 1941 Berger Sept. 5,1950 Pipkin Dec. 13, 1955 Gleim Apr. 2, 1957 Thompson 'July 29, 1958 FOREIGN PATENTS Great Britain Nov. 9,1955 

1. A MOISTURE INDICATING MATERIAL FOR INCLUSION IN THE ENVELOPE OF A LAMP TO INDICATE BY CHANGE IN COLORATION THE PRESENCE OF AIR THEREIN, SAID INDICATING MATERIAL BEING COMPOSED OF A MIXTURE CONSISTING SUBSTANTIALLY OF COBALTOUS-COBALTIC CYANIDE AND 5-80% BY WEIGHT OF A BINDER OF BARIUM CHLORIDE. 